1. Field of the Invention
The present invention relates to halide laser glass and a laser device utilizing the glass. In particular, the halide laser glass and the laser device utilizing the glass according to the present invention can be used in medical lasers, light source lasers for optical communication and optical measurement, and the like.
2. Prior Art
Light having 3 .mu.m-band wavelength which coincides with water-absorption band wavelength has been utilized in medical lasers such as a laser surgical knife and the like in recent years. Further, the light has been utilized in light source lasers (requiring low loss) for optical communication and optical measurement, and the like, because the wavelength is long as 3 .mu.m.
Examples of the laser having an oscillation wavelength of about 3 .mu.m include crystal lasers such as an Er-CaF.sub.2 laser (oscillation wavelength: 2.8 .mu.m), an Er-YLiF.sub.4 laser (oscillation wavelength: 2.8 .mu.m) and an Er-YAG laser (oscillation wavelength: 2.94 .mu.m). Further, in recent years, laser glass (oscillation wavelength: 2.78 .mu.m) prepared by doping fluoride glass mainly containing zirconium fluoride with Er ions has been found [Electronics Letters, vol. 24, page 320, 1988].
Further, it has been discussed that laser glass prepared by doping Th-containing fluoride glass with Er ions and Ho ions may be applied to a 2 .mu.m-band Ho laser [IEE J. Quantum Electronics, vol. 25, page 88, 1989].
Of those lasers, the fluoride glass doped with Er ions has an advantage in that a uniform and large-size material can be obtained relatively easily compared with the crystal lasers. In general, the oscillation threshold can be reduced by increasing the concentration of Er ions used for doping the matrix glass. Accordingly, the fluoride glass has an advantage in that the concentration of Er ions in the fluoride glass can be increased easily by increasing the proportion of Er compounds (ErF.sub.3) used as a raw material, if the concentration can be established to be within a certain range.
However, the conventional laser glass prepared by doping fluoride glass mainly containing zirconium fluoride, with Er ions has a disadvantage in that the amount of ErF.sub.3 as a material for Er ions used for doping the matrix glass is limited to about 6 mol %. The reason is as follows. When the ErF.sub.3 content is not less than 6 mol %, the glass is crystallized so easily that glass as a good laser medium cannot be obtained. Accordingly, it is difficult that the oscillation threshold of the aforementioned laser glass is further reduced by increasing the concentration of Er ions used for doping.
Further, the aforementioned laser glass has a problem in that the laser glass is too low in mechanical strength and chemical durability to be put into practice, because fluoride glass mainly containing zirconium fluoride is used as a matrix.
Further, the glass prepared by doping Th-containing fluoride glass, with Er and Ho ions has a problem in that the glass is danger for a person, because the essential component Th of the glass is a radioactive substance.